The present invention generally relates to an apparatus for transfer wafer from a wafer storage pod to a wafer process machine and more particularly, relates to a wafer transfer robot having a plurality of wafer blades each equipped with a sensing device for sensing the type of wafer it carries.
A wet bench process is frequently carried out after a chemical process has been conducted on a semiconductor wafer. When residual chemical must be removed, deionized water rinse is used in a wet bench process for semiconductor wafer processing to perform two major functions of a quick dump rinse (QDR) and a cascade overflow rinse. Conventionally, the two functions are carried out in separate tanks in order to produce the desirable result. One of the major processing issues presented by the conventional dual-tank process is the particle re-deposition problem during a withdrawal step when cassettes are transported from a quick dump rinse tank to a cascade overflow tank. A second major issue is the large floor space required for accommodating the two tanks.
A conventional wet bench wafer cleaning process is shown in FIG. 1. The wet bench wafer cleaning process 10 for cleaning wafer 12 is carried out in six separate cleaning and rinsing tanks sequentially of a HF cleaning tank 14, a first quick dump rinse (QDR) tank 16, a SC-1 cleaning tank 18, a second quick dump rinse tank 20, a SC-2 cleaning tank 22 and a third quick dump rinse tank 24. The first HF cleaning tank is used to hold a diluted HF solution, for instance, at a concentration of 0.5% HF in H2O for removing a thin native oxide layer from the wafer surface. After the diluted HF cleaning process, the wafer 12 is rinsed in a first quick dump rinse tank 16 with deionized water. Wafer 12 is then cleaned in a second cleaning tank filled with SC-1 cleaning solution, i.e. a mixture of NH4OH, H2O2 and DI water at a ratio of 1:1:5. The SC-1 cleaning solution is used at a temperature between 70-80xc2x0 C. for a suitable time period. The wafer 12 is then rinsed again in a second quick dump rinse tank 20 that is filled with DI water. In the final stage of cleaning, the wafer 12 is cleaned in tank 22 filled with a cleaning solution of SC-2 which is a mixture of HCl, H2O2 and DI water at a ratio of 1:1:6. The wafer 12 is then rinsed in a third quick dump rinse tank 24 with DI water.
The wet bench wafer cleaning process 10 shown in FIG. 1 is conventionally used for pre-diffusion clean, pre-gate oxidation clean, pre-CVD clean, etc. For instance, in the ULSI fabrication of integrated devices, the conventional wet bench wafer cleaning process 10 can be advantageously used for wafer surface cleaning before a coating process in a CVD chamber or an oxidation process in a furnace. The wet bench process shown in FIG. 1 is therefore generally used for front-end processing of a semiconductor wafer.
FIG. 2 is an exploded, perspective view of the conventional wet bench system 10 of FIG. 1 complete with a wafer transfer robot 30. The wafer transfer robot 30 is constructed of a robot arm 32 and a plurality of wafer blades 34 for picking-up wafers stored in a cassette pod 36 (partially shown in FIG. 2). After picking-up wafers from the cassette pod 36, the plurality of wafer blades 34 are turned 90xc2x0 by the robot arm 32 for delivering the wafers into a wafer storage station 38 for the wet bench system 10. A second robot (not shown) then delivers the wafers into the plurality of liquid tanks 40 shown in FIG. 2 for chemical processing of the wafers. Lifters 42 are used for lowering the wafers into and out of the liquid stored in tanks 40.
FIG. 3 shows a close-up view of the wafer transfer robot 30, the plurality of wafer blades 34 and the robot arm 32. The wafer storage station 38 for the wet bench system 10 is also shown in FIG. 3.
In a semiconductor processing facility, wet bench cleaning or etching is also required for the back-end of processing of wafers. For instance, after the deposition of metal layers in forming various via plugs and interconnects. In the wet bench system used in cleaning the back-end wafers, there are always metal particles or metal ions present in the chemical tanks which are absent in the chemical tanks used in cleaning front-end wafers. Since the wet bench cleaning stations are normally grouped together in a semiconductor fabrication facility, i.e for ease of control of chemical dispensing and disposal of used chemicals, the wet bench process lines used for the front-end processing and for the back-end processing must be clearly distinguished. When a batch of wafers intended for front-end wet bench process is mistakenly loaded into a wet bench station used for back-end process, serious contamination of the wafers by metal ions or particles can result in the scrap of the entire lot of wafers. The cost of such mistake is extremely high and can be detrimental to the throughput of an IC device.
Conversely, when a batch of wafers intended for back-end wet bench process is mistakenly placed in a wet bench station for front-end process, the metal layers present on the wafers contaminates the chemical tanks which is very costly and time consuming to clean and replace such that they can be used for processing front-end wafers.
It is therefore an object of the present invention to provide an apparatus for transferring wafers into a wet bench station that does not have the drawbacks or shortcomings of the conventional transfer apparatus.
It is another object of the present invention to provide a wafer transfer robot for a wafer processing system capable of identifying the type of wafer it carries.
It is a further object of the present invention to provide a wafer transfer robot for a wafer processing system that is equipped with wafer blades capable of identifying the type of wafer carried on the blade.
It is another further object of the present invention to provide a wafer transfer robot equipped with a plurality of wafer blades wherein each of the blades is equipped with a sensing device.
It is still another object of the present invention to provide a wafer transfer robot equipped with a plurality of wafer blades each adapted for picking-up a wafer and identifying the wafer as a front-end processed wafer or a back-end processed wafer.
It is yet another object of the present invention to provide a wafer transfer robot equipped with a plurality of wafer blades each equipped with a sensing means capable of sensing whether a wafer it carries has metal layers on top.
In accordance with the present invention, a wafer transfer robot equipped with a plurality of wafer blades each equipped with a sensing device and a method for using the wafer transfer robot are disclosed.
In a preferred embodiment, a wafer transfer robot for a wafer processing system is provided which includes a robot arm equipped with a plurality of wafer blades each adapted for picking-up and carrying one of a plurality of wafers; the plurality of wafer blades each having a predetermined thickness, a top surface, a bottom surface and a predetermined spacing from adjacent robot blades; and a plurality of sensors with at least one mounted on the bottom surface of one of the plurality of wafer blades for sensing the presence of metal on a wafer carried on an adjacent wafer blade immediately below the one of the plurality of wafer blades.
In the wafer transfer robot for a wafer processing system, the wafer processing system may be a wet bench station. The plurality of wafer blades are formed of a metal that does not generate contaminating particles, or formed of aluminum. The predetermined spacing from adjacent wafer blades is between about 3 mm and about 15 mm, and preferably between about 7 mm and about 12 mm. The plurality of sensors are optical sensors for sensing a reflectance of light from a top surface of a wafer that is positioned immediately below the one of the wafer blades. The plurality of sensors may be capacitance sensors for sensing the presence of metal on a top surface of a wafer that is positioned immediately below the one of the wafer blades. The plurality of sensors may also be magnetic sensors. The wafer processing system may be a wet bench for front-end processing of wafers that do not contain any metal layers.
The present invention is further directed to a method for transferring a wafer into a wet bench processing system which can be carried out by the operating steps of first providing a wafer transfer robot that includes a robot arm equipped with a plurality of wafer blades each adapted for picking-up and carrying one of a plurality of wafers; the plurality of wafer blades each has a predetermined thickness, a top surface, a bottom surface and a predetermined spacing from adjacent wafer blades; a plurality of sensors with at least one mounted on the bottom surface of one of the plurality of wafer blades; picking-up at least one wafer by the wafer transport robot from a wafer storage pod; sensing by the at least one sensor a presence of metal on a top surface of a wafer carried on an adjacent wafer blade immediately below the one of the plurality of wafer blades; and signaling an alarm and stopping the wet bench process.
The method for transferring a wafer into a wet bench processing system may further include the step of providing the plurality of sensors in optical sensors, or in capacitance sensors. The method may further include the step of providing the robot arm and the plurality of wafer blades in a metal that does not generate contaminating particles during operation. The present invention is still further directed to a wet bench system for processing semiconductor wafers which includes a first wafer transfer robot that has a robot arm equipped with a plurality of wafer blades each adapted for picking-up and carrying one of a plurality of wafers; the plurality of wafer blades each has a predetermined thickness, a top surface, a bottom surface and a predetermined spacing from adjacent wafer blades; a plurality of sensors with at least one mounted on the bottom surface of one of the plurality of wafer blades for sensing the presence of metal on a wafer carried on an adjacent wafer blade immediately below the one of the plurality of wafer blades; a plurality of liquid tanks for holding quantities of etchants and rinse solutions; and a second wafer transfer robot for removing the wafers from the wet bench system.
In the wet bench system for processing semiconductor wafers, the predetermined spacing from adjacent wafer blades is between about 3 mm and about 15 mm, and preferably between about 7 mm and about 12 mm. The plurality of sensors may be optical sensors, or magnetic sensors for sensing the presence of metal from a top surface of a wafer positioned immediately below the wafer blade. The wet bench system may be a wet bench for front-end processing of wafers that do not contain any metal layers.